This invention relates generally to the field of in place formation of concrete pipes in an open trench for utilization in the transporting of water, sewage, irrigation, etc. Typically, a passageway for transporting any liquid or gas is constructed by the connection of several sections of precast cementitious or concrete pipe which are placed in an open trench and covered. Such precast concrete pipe results in a large amount of joint junctures which must be properly sealed and pose potential leakage areas. Furthermore, the utilization of precast pipe is quite expensive and its placement in the trench is very time consuming.
In the prior art some devices are disclosed which provide for the in place formation of a continuous concrete pipe. However, most of these devices are quite complicated in their construction and operation and do not provide a satisfactory end product for several reasons. One primary problem relates to the lack of proper compaction in the placement of the concrete around the form area, so that there are no weak spots or leakage areas in the continuous run of the in place pipe. This results from the fact that most prior art approaches utilize a gravity feed system in supplying the concrete around the pipe form. Two known prior art devices (Lee, et al, U.S. Pat. No. 3,193,901 and Johnson, et al, U.S. Pat. No. 3,785,759) have considered the placement of concrete in the pipe form under somewhat greater force than gravity. However, both the Johnson ramming device and the Lee auger screw arrangement are extremely complex and expensive in their construction, and believed to be impractical. Furthermore, there is no means available in these devices to check from within the forming apparatus itself the compaction of the concrete at the bottom of the newly formed pipe during the formation process. Consequently, after the concrete has set up sufficiently and the internal support can be removed, defects in the formation of the pipe are noted, requiring someone to patch certain areas where the proper amount of concrete was not placed along the run of the formed pipe.
Another area of significant concern in prior art devices relates to the utilization of a satisfactory and inexpensive support arrangement to occupy the interior area of the pipe and hold it in place while the concrete is being set. Several of these prior art devices use rather complicated fixed form devices which do not provide a smooth interior surface resulting in a variation of pipe internal diameter. Furthermore, the placement of these support devices is time consuming and severely affects the efficiency of the in place forming of the concrete.
Prior art in place concrete forming devices utilize a moving means which is not controlled by the placement of the concrete in the apparatus and, therefore, the apparatus may move forward at a rate which is not proper to provide adequate compaction along the run of the pipe. In many instances, this is due to the fact that, since the trench itself provides the outer form for the concrete pipe, various amounts of concrete are needed as the apparatus proceeds along the trench because of irregular trench configuration. Again when this improper compaction occurs, it is necessary to do patch work after the complete run is finished.
A further problem with prior art devices in this field is directed to the ability to temporarily stop the movement of the apparatus along the trench and then reinstitute movement after a short delay without having to completely remove the device from within the trench. The reason most prior art devices require the removal of the apparatus is to avoid the concrete setting up around the device and locking it within the concrete in the trench.